Pump

ABSTRACT

The pump ( 10, 110, 210 ) may comprise a casing ( 39, 139, 239 ) and a substantially disk-shaped impeller ( 36, 136, 236 ) that rotates within the casing. A group of depression-shaped grooves may be formed on at least one of the front and reverse surfaces of the impeller and the two casing internal surfaces in opposition to these surfaces. The depression-shaped grooves may extend from the center towards the outer periphery of the impeller. When the impeller rotates, fuel within the clearance between the impeller and the casing is propelled, within the depression-shaped grooves, from the center towards the periphery. In this way, forces are generated in the direction that increases the clearance between the impeller and the casing. It is preferred that the group of depression-shaped grooves  38   b  is formed closely spaced near the discharge hole  50  (area B), and elsewhere (area C) is formed more widely spaced. Also, it is preferred that the clearance between the surface on which the depression-shaped grooves  136   c  are formed and the surface  138   b  in opposition thereto increases from the center of the impeller towards the outer periphery of the impeller.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application numbers 2005-341956, 2006-2734 and 2006-126268, the contents of which are hereby incorporated by reference into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a pump for drawing in a fluid such as fuel etc., increasing pressure thereof, and discharging the pressurized fuel.

2. Description of the Related Art

This type of pump normally includes a substantially disk-shaped impeller and a casing that houses the impeller so that the impeller can rotate. On both the front and reverse surfaces of the impeller, a group of concavities is formed. Concavities forming each group are repeated in the circumferential direction. Circular arc-shaped grooves extending from an upstream end to a downstream end are formed in the two casing internal surfaces in the area in opposition to the groups of concavities on the impeller. The pump flow path is formed by the. groups of concavities on the impeller and the circular arc-shaped grooves on the casing. An intake hole is formed in the casing. The intake hole links the upstream end of the pump flow path with the outside of the casing. An discharge hole is formed in the casing. The discharge hole links the downstream end of the pump flow path with the outside of the casing. When the impeller rotates within the casing, fluid is drawn from the intake hole into the pump flow path. Fluid that is drawn into the pump flow path is pressurized while flowing to the downstream end of the pump flow path. The pressurized fluid is expelled outside the casing from the discharge hole.

In this pump, the pressure acting on the front and reverse surfaces of the impeller tends to be non-uniform. Also, the difference in pressure acting on the front and reverse surfaces of the impeller tends to be non-uniform according to position in the circumferential direction. For example, fluid is drawn into the pump flow path within the casing from the intake hole, is pressurized within the pump flow path, and is expelled from the discharge hole. At the upstream end of the pump flow path connecting with the intake hole, fuel is drawn in from one surface of the impeller, but fuel is not drawn in from the other surface. Also, at the downstream end of the pump flow path connected to the discharge hole, fuel is expelled from one surface of the impeller, but fuel is not expelled from the other surface of the impeller. As a result, near the intake hole and discharge hole the difference in pressure acting on the front and reverse surfaces of the impeller becomes larger. If the difference in pressure acting on the impeller varies with position in the circumferential direction the impeller will incline with respect to the axis of the impeller, and contact between impeller and casing will occur. If the impeller continues rotating in this condition, the performance of the pump will be reduced by friction losses and wear.

Therefore, in the pump disclosed in Japanese Laid-open Patent Publication No.6-280776, depression-shaped grooves in a U-shape are formed in both the front and reverse surfaces of the impeller. In this pump, when the impeller rotates, fluid flows into these depression-shaped grooves. When the fluid that has flowed into the depression-shaped grooves is discharged from the depression-shaped grooves, a component of velocity in the axial direction of the impeller is produced. Therefore, the fluid that is discharged from the depression-shaped grooves presses the casing internal surface in the axial direction. In this way, a force is generated that acts in the direction to increase the clearance between the impeller and the casing internal surface, contact between the impeller and the casing is prevented, and the pump efficiency is improved. However, it is difficult to prevent inclination of the impeller by simply forming depression-shaped grooves in the impeller, and it was not possible to prevent sufficiently contact between the impeller and the casing.

BRIEF SUMMARY OF THE INVENTION

It is, accordingly, an object of the present teachings to provide a pump capable of effectively suppressing contact between the impeller and the casing.

In one aspect of the present teachings, a pump may comprise a casing, and a substantially disk-shaped impeller that rotates within the casing. A group of concavities may be formed on both front and reverse surfaces of the impeller. Concavities forming each group may be repeated in a circumferential direction of the impeller. A first groove may be formed on a first casing internal surface in opposition to the front surface of the impeller. The first groove may extend from an upstream end to a downstream end in an area facing one of the groups of concavities of the impeller. A second groove may be formed on a second casing internal surface in opposition to the reverse surface of the impeller. The second groove may extend from an upstream end to a downstream end in an area facing the other of the groups of concavities of the impeller. An intake hole and a discharge hole may be formed in the casing. The intake hole may link the upstream end of one of the first groove and the second groove with the outside of the casing, and the discharge hole may link the downstream end of the other of the first groove and the second groove with the outside of the casing. Therefore, when the impeller rotates, fluid is drawn into the casing from the intake hole. The fluid drawn into the casing is pressurized by the impeller, and is expelled outside the casing from the discharge hole.

In one aspect of the present teachings, a group of depression-shaped grooves may be formed in at least the first and second casing internal surfaces. Each of depression-shaped grooves may extend from the center towards the outer periphery while shifting in the direction of rotation of the impeller. The group of depression-shaped grooves may be asymmetrically formed with respect to the axis of rotation of the impeller in accordance with the position of the first and second grooves.

In this pump, when the impeller rotates, fluid in the clearance between the impeller and the casing is drawn into the group of depression-shaped grooves, and propelled from the center towards the outer periphery. This direction is the same as the direction of the centrifugal force acting on the fluid in the clearance between the impeller and the casing. Therefore, when the impeller rotates, a force that propels the fluid within the group of depression-shaped grooves from the center towards the outer periphery is efficiently generated. The fluid that is propelled from the center towards the outer periphery within the group of depression-shaped grooves presses on the surface of the casing in opposition to the impeller, and generates an effective lift force (i.e., a force acting in the direction to increase the clearance between the impeller and the casing internal surface) on the impeller.

Also, the groups of depression-shaped grooves are formed asymmetrically in accordance with the position of the first groove and the second groove formed on the casing internal surfaces. By forming the group of depression-shaped grooves asymmetrically, it is possible to vary the magnitude of the lift force generated on the impeller according to the area on the impeller. By forming the group of depression-shaped grooves asymmetrically according to the position of the first groove and the second groove, it is possible to increase the lift force generated on the impeller in the areas where the pressure difference is large, and to decrease the lift force generated on the impeller in the areas where the pressure difference is small. In this way, it is possible to eliminate the non-uniformity in the pressure difference between the front and reverse surfaces of the impeller. In this way, it is possible to suppress the inclination of the impeller with respect to the axis of the impeller, and suppress contact between the impeller and the casing.

Forming the groups of depression-shaped grooves asymmetrically may be achieved, for example, by forming areas where the adjacent grooves are closely spaced and areas where the grooves are more widely spaced, or forming areas where the length of grooves is long and areas where the length of grooves is short, or forming areas where the depth of grooves is deep and areas where the depth of grooves is shallow, or forming areas where the width of grooves is wide and areas where the width of grooves is narrow, or forming areas where there are grooves and areas where there are none.

In the above pump, it is preferred that in the area near the discharge hole in the casing internal surface and/or in the area near the intake hole in the casing internal surface, the lift forces generated on the impeller by the group of depression-shaped grooves are greater than in other areas.

Fluid is drawn into the casing from the intake hole, pressurized within the casing and expelled from the discharge hole. Therefore, near the intake hole and the discharge hole the difference in pressure acting on the front and reverse surfaces of the impeller tends to be large. If the group of depression-shaped grooves is formed so that the lift force generated on the impeller in the area near the intake hole and/or the discharge hole is larger than in other areas the pressure difference that varies with the area can be effectively cancelled out.

Alternatively, the group of depression-shaped grooves that generates lift forces on the impeller may be formed in the area near the discharge hole and/or the area near the intake hole only. According to this configuration, lift forces act only on the impeller in the area near the discharge hole and/or in the area near the intake hole, so it is possible to effectively cancel out the pressure difference that varies with the area.

It is preferably that each depression-shaped groove comprising the group of depression-shaped grooves extends from the center of the impeller towards the outer periphery in a spiral shape. By forming the grooves in a spiral shape from the center towards the outer periphery it is possible to smoothly draw the fluid into the grooves.

In another aspect of the present teachings, in at least one surface from among the front and reverse surfaces of the impeller and the first and second casing internal surfaces, depression-shaped grooves may be formed so that fluid in the clearance between the impeller and the casing is pressurized and a force is generated in the direction that increases the clearance between the impeller and the casing when the impeller rotates. Also, the clearance between the surface on which the depression-shaped grooves are formed and the surface in opposition thereto when the impeller is not inclined with respect to the casing may increase from the center of the impeller towards the outer periphery of the impeller.

In this pump, the clearance between the surface on which the depression-shaped grooves are formed and the surface in opposition to this surface increases towards the outer periphery of the impeller. Therefore, even if the impeller inclines slightly, the outer periphery of the impeller and the casing internal surface will not contact. On the other hand at the center of the impeller the clearance between the surface on which the depression-shaped grooves are formed and the surface in opposition to this surface is small. The lift force (i.e., force acting in the direction to increase the clearance between the impeller and the casing) generated by the fluid within the depression-shaped grooves increases the smaller the clearance. Therefore, it is possible to increase the lift force generated by the fluid within the depression-shaped grooves In this way, it is possible to prevent large inclination of the impeller, and contact of the impeller and casing can be suppressed.

In this pump, it is preferred that one surface from among the surface in which the depression-shaped grooves is formed and the surface in opposition thereto is formed as a flat plane, and the other surface is formed in a tapered shape so that the clearance with the impeller increases from the center of the impeller towards the outer periphery of the impeller. According to this configuration, one surface from among the surface in which the depression shaped grooves are formed and the surface that is in opposition to this surface is formed as a flat plane, so processing of this plane is simple.

It is preferred that the depression-shaped grooves extend from the center of the impeller towards the outer periphery in a spiral shape. Also, the depression-shaped grooves may be formed on the impeller or on the casing.

In another aspect of the present teachings, an intake hole and a discharge hole may be formed in the casing. The intake hole links the upstream end of a pump flow path formed by the groups of concavities, the first groove, and the second groove with the outside of the casing. The discharge hole links the downstream end of the pump flow path with the outside of the casing. Depression-shaped grooves sealed from the pump flow path may be formed on at least one surface from among the intake hole side impeller surface and the intake hole side casing internal surface, and depression-shaped grooves sealed from the pump flow path may be formed in neither the discharge hole side impeller surface nor the discharge hole side casing internal surface.

In this type of pump, the force due to the pressure difference of the fluid in the pump flow path acts in a direction to press the impeller towards the intake hole side casing internal surface. In other words, the fluid drawn into the pump flow path is pressurized as it flows from the upstream side (i.e., intake hole side) of the pump flow path to the downstream side (i.e., discharge hole side). Therefore, the fluid in the pump flow path is at a higher pressure in the discharge hole side than the intake hole side Therefore, the surface of the discharge hole side of the impeller is subjected to a higher pressure than the surface of the intake hole side, so the impeller is subject to a force in the direction of the intake hole side casing internal surface.

In this pump, depression-shaped grooves are not formed on the discharge hole side of the impeller surface or the discharge hole side of the casing internal surface. Therefore, a lift force is not generated on the discharge hole side impeller surface; a lift force is only generated on the intake hole side impeller surface. The lift force acting on the intake hole side impeller surface acts in a direction to cancel out the force (i.e., force acting in the direction to press the impeller towards the intake hole side casing internal surface) generated by the difference in pressure of the fluid in the casing. In this way, pressing the impeller towards and contact with the intake hole side casing internal surface, is suppressed.

In this pump, it is preferred that a projecting portion is formed in the discharge hole side casing internal surface forming a loop in the circumferential direction of the impeller. If a projecting portion is formed in the discharge hole side casing internal surface, even if there is contact between the discharge hole side casing internal surface and the impeller, the discharge hole side casing internal surface and the impeller only contact locally. Therefore, it is possible to reduce the friction losses when the impeller and casing contact.

Further, it is preferred that the projecting portion is positioned to the inside of the pump flow path. By providing the projecting portion to the inside of the pump flow path it is possible to suppress leakage of fluid from the pump flow path that passes the projecting portion and flows into the clearance on the discharge hole side. In this way, it is possible to efficiently pressurize of the fluid within the casing, and the pump performance can be improved.

Also, this pump may further include a motor chamber provided on the outside of the casing and a motor housed within the motor housing. The motor may have a shaft that rotates. In this case, it is preferred that the discharge hole links the pump flow path and the motor chamber and a through hole that is penetrated by the motor shaft are formed in the casing, and one end of the motor shaft is fitted to the impeller.

According to this configuration, the impeller is subject to a force in the direction of the intake bole side casing internal surface as a result of high pressure fluid that flows backwards from the motor chamber into the casing via the gap between the shaft and the through hole. As a result, contact between the impeller and the discharge hole side casing internal surface is suppressed. Also, even if the impeller is subject to a force in the direction of the intake hole side casing internal surface, the lift force generated by the depression-shaped grooves acts in the direction to cancel out that force, so contact between the impeller and the intake hole side casing internal surface is suppressed.

In another aspect of the present teachings, an intake hole and a discharge hole may be formed in the casing. The intake hole may link the upstream end of a pump flow path formed by the groups of concavities, the first groove, and the second groove with the outside of the casing. The discharge hole may link the downstream end of the pump flow path with the outside of the casing. Intake hole side depression-shaped grooves may be formed on at least one surface from among the intake hole side impeller surface and the intake hole side casing internal surface so that when the impeller rotates fluid is pressurized and a lift force is generated that acts in the direction to increase the clearance between the intake hole side impeller surface and the intake hole side casing internal surface. Discharge hole side depression-shaped grooves may be formed on at least one surface from among the discharge hole side impeller surface and the discharge hole side casing internal surface so that when the impeller rotates fluid is pressurized and a lift force is generated that acts in the direction to increase the clearance between the discharge hole side impeller surface and the discharge hole side casing internal surface. The number and/or shape of the discharge hole side depression-shaped grooves are preferably determined so that the lift force generated is smaller than the lift force generated by the intake hole side depression-shaped grooves, in accordance with the number and/or shape of the intake hole side depression-shaped grooves.

According to this pump also, it is possible to suppress pressing the impeller towards and contact with the intake hole side casing internal surface.

These aspects and features may be utilized singularly or, in combination, in order to make improved pump. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and claims. Of course, the additional features and aspects disclosed herein also may be utilized singularly or, in combination with the above-described aspect and features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section through a pump according to a first representative embodiment of the present teachings.

FIG. 2 is a section through the line II-II in FIG. 1.

FIG. 3 is a section on the line III-III in FIG. 1.

FIG. 4 is a view corresponding to the section through the line II-II in FIG. 1 for a pump according to a second representative embodiment of the present teachings.

FIG. 5 is a view corresponding to the section through the line III-III in FIG. 1 for a pump according to a second representative embodiment of the present teachings.

FIG. 6 is a diagram to explain an example of the depression-shaped grooves formed on the pump casing.

FIG. 7 is a diagram to explain another example of the depression-shaped grooves formed on the pump casing.

FIG. 8 is a section on the line VIII-VIII in FIG. 7.

FIG. 9 is a section on the line IX-IX in FIG. 7.

FIG. 10 is a vertical section through a pump according to a third representative embodiment of the present teachings.

FIG. 11 is a plan (of the discharge hole side surface) of the impeller of the pump shown in FIG. 10.

FIG. 12 is a view to explain the shape of the grooves formed in the discharge hole side surface of the impeller shown in FIG. 11.

FIG. 13 is a section showing an enlargement of the pump according to the third representative embodiment.

FIG. 14 is a vertical section through a pump according to a fourth representative embodiment of the present teachings.

FIG. 15 is a plan view of the impeller of the fourth representative embodiment viewed from the bottom.

FIG. 16 is a diagram to explain the shape of the grooves formed in the bottom surface of the impeller shown in FIG. 15.

FIG. 17 is a section showing an enlargement of the pump according to the fourth representative embodiment of the present teachings.

FIG. 18 is a section showing an enlargement of the Dump according to a fifth representative embodiment of the present teachings.

FIG. 19 is a plan of the impeller according to the fifth representative embodiment viewed from the bottom.

FIG. 20 is a plan showing another example of the depression-shaped grooves formed in the top surface of the impeller.

FIG. 21 is a plan showing another example of the depression-shaped grooves formed in the top surface of the impeller.

FIG. 22 is a plan showing another example of the depression-shaped grooves formed in the top surface of the impeller.

FIG. 23 shows the schematic relationship between the direction of the depression-shaped grooves and the direction of flow of the fuel within the clearance.

DETAILED DESCRIPTION OF THE INVENTION First Representative Embodiment

A Wesco pump 10 according to a first representative embodiment of the present teachings is explained with reference to the drawings. The Wesco pump 10 may be used as fuel pump for an automobile. The Wesco pump 10 may be utilized within a fuel tank, being utilized for supplying fuel to an engine of the automobile.

As shown in FIG. 1, the Wesco pump 10 includes a motor unit 12 and a pump unit 14. The motor unit 12 has a rotor 18. The rotor 18 includes a shaft 20, a laminated iron core 22 fixed to the shaft 20, a coil (not shown in the drawings) wound around the laminated iron core 22, and a commutator 24 connected to the ends of the coil. The shaft 20 is rotatably supported by a housing 16 via bearings 26, 28. A permanent magnet 30 is fixed to the inside of the housing 16 so as to surround the rotor 18. Terminals which are not shown on the drawings are provided on a top cover 32 attached to the top of the housing 16, to supply electricity to the motor unit 12. The coil is activated via a brush 34 and the commutator 24, to rotate the rotor 18 and shaft 20.

The lower part of the housing 16 houses the pump unit 14. The pump unit 14 includes a substantially disk-shaped impeller 36. On the top surface of the impeller 36, a group of concavities 3 a is formed along the outer periphery. On the bottom surface of the impeller 36, a group of concavities 3 b is formed along the outer periphery. A through hole is formed in the center of the impeller 36, connected to the shaft 20 so as to prevent relative rotation.

A pump casing 39 that houses the impeller 36 includes a pump cover 38 and a pump body 40.

As shown in FIG. 2, a groove 38 a is formed in the pump cover 38 in the area in opposition to the group of concavities 36 a. The groove 38 a is formed in an approximately C-shape stretching from the upstream end to the downstream end along the direction of rotation of the impeller 36. An discharge hole 50 is formed in the pump cover 38 from the downstream end of the groove 38 a to the top surface of the pump cover 38. The discharge hole 50 links the interior of the pump casing 39 with the exterior (i.e., the internal space of the motor unit 12). A first pump flow path 44 is formed by the group of concavities 36 a and the groove 38 a. A group of depression-shaped grooves 38 b, 38 b, . . . is provided on the bottom surface of the pump cover 38 centralized in the radial direction. The group of depression-shaped grooves 38 b, 38 b, . . . is described later.

As shown in FIG. 3, a groove 40 a is formed in the pump body 40 in the area in opposition to the group of concavities 36 b. Similar to the groove 38 a, the groove 40 a is formed in an approximate C-shape stretching from the upstream end to the downstream end along the direction of rotation of the impeller 36. An intake hole 42 is formed in the pump body 40 from the bottom surface of the pump body 40 to the upstream end of the groove 40 a The intake hole 42 links the interior of the pump casing 39 and the exterior (i.e., exterior of the Wesco pump 10). A second pump flow path 46 is formed by the group of concavities 38 b and the groove 40 a. A group of depression-shaped grooves 40 b, 40 b, . . . is provided in the top surface of the pump body 40 centralized in the radial direction. The group of depression-shaped grooves 40 b, 40 b, . . . is described later.

When the impeller 36 rotates within the pump casing 39, fuel is drawn in from the intake hole 42 into the pump unit 14 and is led to the pump flow paths 44, 46. The fuel is pressurized while flowing along the fuel flow paths 44, 46, and is propelled from the discharge hole 50 towards the motor unit 12. The fuel propelled towards the motor unit 12 passes the motor unit 12, and is expelled to the outside from a discharge port 48 formed in the top cover 32.

As shown in FIG. 2, the group of depression-shaped grooves 38 b, 38 b, . . . formed in the pump cover 38 all have the same shape and size. The depression-shaped grooves 38 b extend from near the center towards the periphery in a curved shape (spiral shape). The ends of the depression-shaped grooves 38 b near the periphery are shifted in the direction of rotation of the impeller 36 (in the direction of the arrow A) relative to the ends near the center.

The interval between adjacent depression-shaped grooves 38 b varies depending on the area in which the grooves are formed. The depression-shaped grooves 38 b, 38 b, . . . formed in the area B with the discharge hole 50 in the center (one end of the area B extends to the upstream end of the groove 38 a) are formed more closely spaced than the depression-shaped grooves 38 b, 38 b, . . . formed in the area C which is the area outside area B. A distance D is provided between the outer periphery end of the depression-shaped grooves 38 b and the inner edge of the groove 38 a. In other words, a flat plane doughnut shape of width D is formed between the outer periphery ends of the depression-shaped grooves 38 b, 38 b, . . . and the inner edge of the groove 38 a. The depression-shaped grooves 38 b, 38 b, . . . and the groove 38 a are sealed by this flat plane.

As shown in FIG. 3, the group of depression-shaped grooves 40 b, 40 b, . . . formed in the pump body 40 all have the same shape and size. The depression-shaped grooves 40 b extend from the near the center towards the periphery in a curved shape (spiral shape). The ends of the depression-shaped grooves 40 b near the periphery are shifted in the direction of rotation of the impeller 36 (in the direction of the arrow E) relative to the end near the center.

The interval between adjacent depression-shaped grooves 40 b varies depending on the area in which the grooves are formed. The depression-shaped grooves 40 b, 40 b, . . . formed in the area F with the downstream end of the groove 40 a in the center (one end of the area F extends to the intake hole 42) are formed more closely spaced than the depression-shaped grooves 40 b, 40 b, . . . formed in the area G which is the area outside area F. A distance H is provided between the outer periphery end of the depression-shaped grooves 40 b and the inner edge of the groove 40 a. In other words, a flat plane doughnut shape of width H is formed between the outer periphery ends of the depression-shaped grooves 40 b, 40 b, . . . and the inner edge of the groove 40 a.

In the Wesco pump 10 according to the present representative embodiment, a group of depression-shaped grooves 38 b, 38 b. . . and a group of depression-shaped grooves 40 b, 40 b, . . . are formed in the pump cover 38 and the pump body 40 respectively. When the impeller 36 rotates the fuel in the clearance between the impeller 36 and the pump casing 39 is drawn into the group of depression-shaped grooves 38 b, 38 b, . . . and the group of depression-shaped grooves 40 b, 40 b. . . The outer ends of the depression-shaped grooves 38 b, 40 b are shifted in the direction of rotation of the impeller 36 relative to the inner ends. Therefore, when the impeller 36 rotates, the direction of the viscous forces that draws the fuel into the depression-shaped grooves 38 b, 40 b acts from the center of the impeller 36 towards the Outer periphery. This direction is the same as the direction of the centrifugal force acting on the fuel within the clearance between the impeller 36 and the pump casing 39 when the impeller 36 rotates.

Therefore, when the impeller 36 rotates a force is generated that efficiently propels the fuel within the depression-shaped grooves 38 b, 40 b in the direction from the center towards the periphery. The impeller 36 is pressed from both the top and bottom surfaces by the fuel propelled from the center towards the outer periphery within the group of depression-shaped grooves 38 b, 38 b, . . . and the group of depression-shaped grooves 40 b, 40 b, . . . , so the impeller 36 is maintained between the pump cover 38 and the pump body 40.

Also, in the pump cover 38 the group of depression-shaped grooves 38 b, 38 b, . . . is closely spaced near the discharge hole 50 (area B), and elsewhere (area C) the group of depression-shaped grooves 38 b, 38 b, . . . is more widely spaced. In the pump body 40 the group of depression-shaped grooves 40 b, 40 b, . . . is closely spaced near the downstream end of the groove 40 a (area F), and elsewhere (area G) the group of depression-shaped grooves 40 b, 40 b, . . . is more widely spaced. In areas B and F where the grooves are closely spaced, more fuel is propelled from the center to the outer periphery, so the forces acting on the impeller 36 are greater, and the difference in pressure on the top and bottom surfaces of the impeller 36 is cancelled out. In this way it is possible to suppress the inclination of the impeller 36 with respect to the axis, and contact between the impeller 36 and the pump casing 39 can be suppressed. Also, in the areas C and G where the grooves are widely spaced, sealing can be maintained as a result of the large flat surface. As a result inclination of the impeller 36 can be suppressed, and leakage of fuel from the pump flow paths can be reduced.

In this way, according to the Wesco pump 10 of the present representative embodiment friction losses and wear can be reduced, and leakage of fuel from within the pump flow paths can be reduced. Therefore the performance of the pump can be effectively improved.

Second Representative Embodiment

A Wesco pump according to a second representative embodiment is explained with reference to the drawings. The Wesco pump according to the second representative embodiment is constituted similar to the Wesco pump 10 according to the first representative embodiment, and differs from the first representative embodiment only in the configuration of the groups of depression-shaped grooves formed on the pump casing. Here only the points of difference between the second representative embodiment and the first representative embodiment are explained, explanation of common points is omitted.

As shown in FIG. 4, a group of depression-shaped grooves 68 b, 68 b, . . . formed on a pump cover 68 extends from the center towards the periphery in curved lines. The ends of the depression-shaped grooves 68 b near the periphery are shifted in the direction of rotation of the impeller 36 (the direction of arrow J) relative to the ends near the center. The spacings between adjacent depression-shaped grooves 68 b, 68 b. . . are all equal.

There are two types of shape for the depression-shaped grooves 68 b, 68 b, . . . The length of the group of depression-shaped grooves 68 b 1, 68 b 1, . . . formed in the area K with an discharge hole 50 a at the center (one end of area K extends to the upstream end of a groove 68 a), is longer than the length of the group of depression-shaped grooves 68 b 2, 68 b 2, . . . formed in the area L, the area other than the area K, so the ends near the outer periphery are positioned closer to the periphery. In other words, the distance M between the ends of the depression-shaped grooves 68 b 1 near the periphery and the inner edge of the groove 68 a is shorter than the distance N between the ends of the depression-shaped grooves 68 b 2 near the periphery and the inner edge of the groove 68 a. A flat surface is formed in the area between the ends of the group of depression-shaped grooves 68 b, 68 b, . . . near the periphery and the inner edge of the groove 68 a.

As shown in FIG. 5, a group of depression-shaped grooves 70 b, 70 b, . . . formed on a pump cover 70 extends from near the center towards the periphery in curved lines. The ends of the depression-shaped grooves 70 b near the periphery are shifted in the direction of rotation of the impeller 36 (the direction of arrow P) relative to the ends near the center. The spacings between adjacent depression-shaped grooves 70 b, 70 b, . . . are all equal.

There arc two types of shape for the depression-shaped grooves 70 b, 70 b, . . . The length of the group of depression-shaped grooves 70 b 1, 70 b 1, . . . formed in the area Q with the downstream end of a groove 70 a in the center (one end of the area Q extends to an intake hole 40 a) is longer than the length of the group of depression-shaped grooves 70 b 2, 70 b 2, . . . formed in the area R, the area other than the area Q, so the ends near the outer periphery are positioned closer to the periphery. In other words, the distance S between the ends of the depression-shaped grooves 70 b 1 near the periphery and the inner edge of the groove 70 a is shorter than the distance T between the ends of the depression-shaped grooves 70 b 2 near the periphery and the inner edge of the groove 70 a. A flat surface is formed in the area between the ends of the depression-shaped group of grooves 70 b, 70 b, . . . near the periphery and the inner edge of the groove 70 a.

In the Wesco pump according to the second representative embodiment, as for the Wesco pump 10 according to the first representative embodiment, the group of depression-shaped grooves 68 b, 68 b, . . . and the group of depression-shaped grooves 70 b, 70 b, . . . are formed in the pump cover 68 and the pump body 70 respectively. In the pump cover 68, the group of depression-shaped grooves 68 b 1, 68 b 1, . . . near the discharge hole 50 a (area K) are long, and the depression-shaped group of grooves 68 b 2, 68 b 2, . . . formed in the other area (area L) are short. In the pump body 70 the group of depression-shaped grooves 70 b 1, 70 b 1, . . . near the downstream end of the groove 70 a (area Q) are long, and the group of depression-shaped grooves 70 b 2, 70 b 2, . . . in the other area (area R) are short. In areas K and Q where the grooves are formed longer, more fuel is propelled from the center towards the periphery, so the difference in pressure applied to the top and bottom surfaces of the impeller 36 is cancelled out. In this way it is possible to suppress the inclination of the impeller 36 with respect to the axis, and contact between the impeller 36 and the pump casing 68, 70 can be suppressed. Also, in the areas L and R where the grooves are formed short, sealing can be maintained as a result of the large flat surface. As a result, leakage of fuel from the pump flow paths can be reduced.

In both the first and second representative embodiments described above, depression-shaped grooves 38 b, 40 b, 68 b, 70 b are formed in both the areas B, F, K, Q near the intake hole and discharge hole and in the other areas C, G, L, R. However, the present teachings are not limited to this type of configuration. For example, depression-shaped grooves may be formed in the areas near the intake hole and discharge hole to generate forces to cancel out the difference in pressure on the top and bottom surfaces of the impeller as much as possible, but in the other areas the depression-shaped grooves may be omitted. This is because in the areas apart from the areas near the intake hole and discharge hole, the difference in pressure applied to the top and bottom surfaces is very small. By forming groups of depression-shaped grooves only near the intake hole and discharge hole the sealing is further improved, and leakage of fuel from the pump flow paths is effectively reduced.

Also, it is possible to obtain similar effects by varying the shape of the depression-shaped grooves (for example, groove width, groove depth, inflow angle) (see Table 1). For example, as shown in FIG. 6, in area B where the difference in pressure on the top and bottom surface of the impeller is large the width of the depression-shaped groove 88 b can be increased, and in area C where the pressure difference is small the width of the depression-shaped groove 88 b can be decreased. Or, as shown in FIGS. 7 through 9, in area B where the difference in pressure on the top and bottom surface of the impeller is large, the depth t2 of the depression-shaped groove 98 b can be increased (see FIG. 9), and in area C where the pressure difference is small the depth t1 of the depression-shaped groove 98 b can be decreased (see FIG. 8). Furthermore, in the area where the difference in pressure of the top and bottom surfaces of the impeller is large the inflow angle can be made an acute angle, and in the area where the difference in pressure of the top and bottom surfaces of the impeller is small the inflow angle can be made an obtuse angle. TABLE 1 Large pressure Small pressure difference difference Number of grooves Many Few Groove length Long Short Groove width Large Small Groove depth Deep Shallow Inflow angle Acute angle Obtuse angle

Also, in the first and second representative embodiments, depression-shaped grooves are formed in both the pump cover and pump body, but depression-shaped grooves may be formed in either one of the pump cover or the pump body. This is because depending on the type of fluid pressurized by the Wesco pump and the configuration of the intake hole and discharge hole, and the like, forming the depression-shaped grooves in only one of either the pump cover or pump body can suppress the inclination of the impeller.

It is possible to select the number, length, cross-sectional shape of the depression-shaped grooves as appropriate.

Third Representative Embodiment

A Wesco pump 110 according to a third representative embodiment of the present teachings is explained with reference to the drawings. The Wesco pump 110 according to the third representative embodiment has a configuration that is substantially similar to the configuration of the Wesco pump 10 in the first representative embodiment. However, the third representative embodiment differs from the Wesco pump 10 according to the first representative embodiment in that groups of depression-shaped grooves are formed on the impeller, and the clearance between the impeller and the pump casing varies in the radial direction Here the points of difference with the first representative embodiment are explained in detail and the points in common with the first representative embodiment are omitted.

As shown in FIG. 10, the Wesco pump 110 includes a motor unit 112 and a pump unit 114. The motor unit 112 has the same configuration as the motor unit 12 of the Wesco pump 10 according to the first representative embodiment. The pump unit 114 includes a substantially disk-shaped impeller 136 and a pump casing 139 that houses the impeller 136.

As shown in FIG. 11, a D-shaped through hole 138 f is formed in the center of the impeller 136. The through hole 138 f is fitted to the bottom end of the shaft 120. Therefore, the impeller 136 can move in the axial direction of the shaft 120, but cannot rotate relative to the shaft 120. Thus, when the shaft 120 rotates the impeller 136 also rotates.

The top and bottom surfaces of the impeller 136 are formed as planes substantially perpendicular to the shaft 120. On the top surface of the impeller 136, a group of concavities 136 a, 136 a, . . . is formed along the periphery, and a group of depression-shaped grooves 136 c, 136 c, . . . is provided in the central part in the radial direction of the impeller 136. On the bottom surface of the impeller 136, a group of concavities 136 b, 136 b, . . . is formed along the periphery, and a group of depression-shaped grooves 136 d, 136 d, . . . is provided in the central part in the radial direction. Each of the group of concavities 136 a, 136 a, . . . formed in the top surface of the impeller 136 and each of the group of concavities 136 b, 136 b, . . . formed in the bottom surface are linked at the bottom of the concavities.

As shown in FIGS. 11 and 12, the depression-shaped grooves 136 c formed in the top surface of the impeller 136 extend from their end 137 c near the center to their end 137 a near the periphery in a curved shape (spiral shape). Also, a distance A is provided between the end 137 a of the depression-shaped grooves 136 c and the concavities 136 a. In other words, a flat plane is formed between the ends 137 a, 137 a, . . . of the group of depression-shaped grooves 136 c, 136 c, . . . near the periphery and the group of concavities 136 a, 136 a, . . . Furthermore, a flat plane is also formed between the group of concavities 136 a, 136 a, . . . and surface of the periphery 136 e of the impeller 136.

Although not shown on the drawings, the depression-shaped grooves 136 d formed in the bottom surface of the impeller 136 are configured in the same way as the depression-shaped grooves 136 c on the top surface as described above. Also, a flat plane is formed between the ends of the outer periphery of the depression-shaped group of grooves 136 d and the group of concavities 136 b. Furthermore, a flat plane is also formed between the group of concavities 136 b, 136 b, . . . and surface of the periphery 136 e of the impeller 136.

The pump casing 139 includes a pump cover 138 and a pump body 140. A taper is formed on the casing surface 138 b of the pump cover 138 so that the clearance with the impeller 136 increases from the center of the impeller 136 towards the periphery of the impeller 136. A groove 138 a is formed in the casing surface 138 b in opposition to the group of concavities 136 a provided in the top surface of the impeller 136. A taper is also formed on the casing surface 140 b of the pump body 140 so that the clearance with the impeller 136 increases from the center of the impeller 136 towards the periphery of the impeller 136. A groove 140 a is formed in the casing surface 140 b in opposition to the group of concavities 136 b provided in the bottom surface of the impeller 136. The grooves 138 a and 140 a are formed in an approximate C-shape from the upstream end to the downstream end along the direction of rotation of the impeller 136. The upstream end of the groove 140 a is formed to that it links with the intake hole 142 in the pump body 140. The downstream end of the groove 138 a is formed to that it links with the discharge hole 150 in the pump cover 138. A first pump flow path 144 is formed by the group of concavities 136 a formed in the top surface of the impeller 136 and the groove 138 a formed in the pump cover 138. A second pump flow path 146 is formed by the group of concavities 136 b formed in the bottom surface of the impeller 136 and the groove 140 a formed in the pump body 140. In FIGS. 10 and 13, the taper angle on the casing surface 138 b and the casing surface 140 b has been magnified for ease of viewing. In reality the taper angle of the casing surface 138 b and the casing surface 140 b is very small.

When the impeller 136 rotates within the pump casing 139, fuel is drawn into the pump unit 114 from the intake hole 142 and is led into the pump flow paths 144, 146. The fuel that is pressurized while flowing through the pump flow paths 144, 146 is propelled from the discharge hole 150 towards the motor unit 112. The fuel that is propelled towards the motor unit 112 passes the motor unit 112, and is propelled to the outside from a discharge port 148 formed in a top cover 132.

When the impeller 136 rotates, the fuel in the clearance between the impeller 136 and the pump casing 138, 140 is drawn into the group of depression-shaped grooves 136 c, 136 c, . . . and the group of depression-shaped grooves 136 d, 136 d, . . . The fuel that is drawn into the depression-shaped grooves 136 c, 136 c, . . . is guided by the wall 137 b on one side of the depression-shaped grooves 136 c, 136 c, . . . , and flows towards the end 137 a near the outer periphery of the depression-shaped grooves 136 c, 136 c, . . . (refer to FIG. 12). Likewise on the bottom surface of the impeller 136, the fuel is drawn into the group of depression-shaped grooves 136 d, 136 d. . . , and flows within the depression-shaped grooves 136 d, 136 d, . . . towards the ends near the outer periphery. The fuel that is propelled from the center towards the outer periphery within the depression-shaped grooves 136 c, 136 c, . . . and the depression-shaped grooves 136 d, 136 d, . . . pressurizes the casing surface 136 b and the casing surface 140 b, and generates a lift force on the impeller 136 (i.e., a force in the direction that increases the clearance with the casing surface 138 b and with the casing surface 140 b). Contact between the impeller 136 and the casing surface 138 b or the casing surface 140 b is prevented by these lift forces. The lift force acting on the impeller 136 increases as the clearance between the impeller 136 and the pump casing 138, 140 decreases. In the Wesco pump 110 according to the present representative embodiment, the casing surfaces 136 b, 140 b are formed with a taper so that the clearance with the impeller 136 increases from the center of the impeller 136 towards the outer periphery of the impeller 136. In other words, in the locations where the group of depression-shaped grooves 136 c, 136 c, . . . and the group of depression-shaped grooves 136 d, 136 d, . . . are formed the clearance between the impeller 136 and the pump casing 138, 140 is small. Therefore, a larger lift force acts on the impeller 136. In this way, it is possible to further reduce friction losses and wear.

The following is a detailed explanation of the lift force that is generated by the groups of depression-shaped grooves 136 c, 136 c, . . . and 136 d, 136 d, . . . when the impeller 136 rotates. As stated above, when the impeller 136 rotates fuel is led from the intake hole 142 into the pump flow paths 144, 146, and the fuel is pressurized as it flows in the pump flow paths 144, 146. Therefore, the further upstream in the pump flow paths 144, 146 the lower the fuel pressure, and the further downstream in the pump flow paths 144, 146 the higher the fuel pressure. Also, the pump flow paths 144, 146 are formed on the top and bottom surfaces of the impeller 136, so the impeller 136 is subject to a force in the thrust direction as a result of the pressure difference of the fuel flowing in the first pump flow path 144 and the second pump flow path 146. The pressure difference of the fuel flowing in the first pump flow path 144 and the second pump flow path 146 varies according to position in the circumferential direction of the impeller 136. Therefore, the impeller 136 is subject to non-uniform forces, so the impeller 136 inclines a very small amount On the other hand, the casing surfaces 138 b, 140 b of the pump casing 139 are formed with a taper so that the clearance with the impeller 136 increases from the center of the impeller 136 towards the outer periphery of the impeller 136. Therefore, even though the impeller 136 inclines slightly, the periphery of the impeller 136 does not contact the casing surfaces 138 b, 140 b (refer to FIG. 13). Also, if the impeller 136 inclines slightly, part of the group of depression-shaped grooves 136 c, 136 c, . . . (the part on the right hand side in FIG. 13) approaches the casing surface 138 b, and part of the group of depression-shaped grooves 136 d, 136 d, . . . (the part on the left hand side in FIG. 13) approaches the casing surface 140 b. Then at the position where they approach, the pressure of the fuel in the group of depression-shaped grooves 136 c, 136 c, . . . and the group of depression-shaped grooves 136 d, 136 d, . . . increases, so the pressure on the casing surface 138 b and the casing surface 140 b increases. This increased pressure acts in a direction to prevent inclination of the impeller 136, so the impeller 136 returns to a horizontal attitude. Therefore, even if the impeller 136 inclines slightly, the impeller 136 tends to return to the horizontal as a result of the lift forces generated by the group of depression-shaped grooves 136 c, 136 d. Therefore, contact between the impeller 136 and the casing surfaces 138 b, 140 b is prevented, and friction losses and wear can be reduced.

According to the Wesco pump 110 of the present representative embodiment, the lift force of the impeller 136 is increased, so it is possible to suppress friction losses and wear. Also, even if the impeller 136 inclines slightly, contact between the periphery of the impeller 136 and the casing surfaces 138 b, 140 b can be prevented. Also, forces that tend to restore the impeller 136 to the horizontal act on the impeller 136 as a result of the lift forces generated by the depression-shaped grooves 136 c, 136 d. In this way it is possible to effectively improve the performance of the pump.

Also, in the Wesco pump 110 according to the present representative embodiment, the group of depression-shaped grooves 136 c, 136 c, . . . and the group of depression-shaped grooves 136 d, 136 d, . . . are formed on the impeller 136 that rotates, in order to generate lift forces on the impeller 136. Therefore, in addition to centrifugal forces and viscous forces, inertial forces also act on the fuel within the group of depression-shaped grooves 136 c, 136 c, . . . and the group of depression-shaped grooves 136 d, 136 d, . . . As a result of the synergistic effect of these forces, it is possible to generate more effective lift forces.

Also, in the Wesco pump 110 according to the present representative embodiment, the groups of depression-shaped grooves 136 c, 136 d extend from near the center of the impeller 136 towards the outer periphery of the impeller 136 in a curved shape (spiral shape). Therefore, fuel drawn in can more effectively flow towards the periphery, and a greater lift force can be obtained.

In the Wesco pump 110 described above, the group of depression-shaped grooves 136 c, 136 d formed in the impeller 136 extend from near the center of the impeller 136 towards the outer periphery in a curved shape. However, the present teachings are not limited to this form. The number, length, cross-sectional shape, and the like of the depression-shaped grooves formed on the impeller may be selected as appropriate. Also, the groups of depression-shaped grooves 136 c, 136 d may be formed on the casing surfaces 138 b, 140 b.

Also, in the present representative embodiment, the casing surfaces 138 b, 140 b are formed in a tapered shape so that the clearance with the impeller 136 increases from near the center of the impeller 136 towards the outer periphery. However, the present teachings are not limited to this form. For example, the top and bottom surfaces of the impeller 136 may be formed in a taper so that the clearance with the casing surfaces 138 b, 140 b increases from near the center of the impeller 136 towards the outer periphery.

Fourth Representative Embodiment

A Wesco pump 210 according to a fourth representative embodiment is explained with reference to the drawings. The Wesco pump 210 according to the fourth representative embodiment is substantially similar to the Wesco pump 10 according to the first representative embodiment. However, the Wesco pump in the fourth representative embodiment differs from the Wesco pump 10 in the first representative embodiment in that a group of depression-shaped grooves is formed only in the bottom surface of the impeller, and the clearance between the top surface of the impeller and the pump casing varies in the radial direction. Here the points of difference with the first representative embodiment are explained in detail, and the explanation of the points in common with the first representative embodiment are omitted.

As shown in FIG. 14, the Wesco pump 210 includes a motor unit 212 and a pump unit 214. The motor unit 212 is configured in the same way as the motor unit 12 of the Wesco pump 10 according to the first representative embodiment. The pump unit 214 includes a substantially disk-shaped impeller 236 and a pump casing 239 that houses the impeller 236.

The top and bottom surfaces of the impeller 236 are formed in a plane shape substantially normal to a shaft 220. In the top surface of the impeller 236, a group of concavities 236 b, 236 b, . . . is provided continuously in the radial direction along the outer periphery. In the bottom surface of the impeller 236, a group of concavities 236 a, 236 a, . . . is provided continuously in the radial direction along the outer periphery, and a group of depression-shaped grooves 236 c, 236 c, . . . is provided to the inside of the group of concavities 236 a, 236 a, . . . extending from near the center of the impeller 236 towards the outer periphery. The group of concavities 236 b, 236 b, . . . formed in the top surface of the impeller 236 and the group of concavities 236 a, 236 a, . . . formed in the bottom surface are linked at the bottom of the concavities.

As shown in FIGS. 15 and 16, the depression-shaped grooves 236 c formed in the bottom surface of the impeller 236 extend from their end 237 c near the center to their end 237 a near the periphery in a curved shape (spiral shape). Also, a distance A is provided between the end 237 a of the depression-shaped grooves 236 c near the periphery and the concavities 236 a. In other words, a flat plane is formed between the ends 237 a, 237 a, . . . of the group of depression-shaped grooves 236 c, 236 c, . . . near the periphery and the group of concavities 236 a, 236 a, . . . Furthermore, a flat plane is also formed between the group of concavities 236 a, 236 a, . . . and surface of the periphery 236 e of the impeller 236.

The pump casing 239 includes a pump cover 238 and a pump body 240. A casing surface 240 b of the pump body 240 is formed in a plane shape parallel to the bottom surface of the impeller 236. A groove 240 a is formed in the casing surface 240 b in opposition to the group of concavities 236 a, 236 a, . . . provided in the bottom surface of the impeller 236. A casing surface 238 b of the pump cover 238 is formed so that a part of the casing surface 238 b is closest to the impeller 236, as shown in FIG. 17. The part (projecting portion 238 c) that is closest to the impeller 236 is formed as a continuous loop in the circumferential direction. A groove 238 a is formed in the casing surface 238 b in opposition to the group of concavities 236 b, 236 b, . . . provided in the top surface of the impeller 236. The grooves 238 a and 240 a are formed in an approximate C-shape from the upstream end to the downstream end along the direction of rotation of the impeller 236. The upstream end of the groove 240 a is formed to that it links with an intake hole 42 in the pump body 240 The downstream end of the groove 238 a is formed to that it links with a discharge hole 250 formed in the pump cover 238. A first pump flow path 244 is formed by the group of concavities 236 b formed in the top surface of the impeller 236 and the groove 238 a formed in the pump cover 238. A second pump flow path 246 is formed by the group of concavities 236 a formed in the bottom surface of the impeller 236 and the groove 240 a formed in the pump body 240.

When the impeller 236 rotates within the pump casing 239, fuel is drawn into the pump unit 214 from the intake hole 242. Fuel drawn into the pump unit 214 flows from the upstream side to the downstream side of the pump flow paths 244, 246. Also, while the fuel is flowing in the pump flow paths 244, 246, the fuel pressure is increased. When the fuel flowing in the pump flow paths 244, 246 reaches the downstream end of the pump flow path 244, the fuel is expelled from the discharge hole 250 to the motor unit 212. The fuel that is propelled towards the motor unit 212 passes the motor unit 212, and is propelled to the outside from an discharge port 248.

Here, the forces acting on the impeller 236 when the impeller 236 rotates are explained. As stated above, when the impeller 236 rotates, the fuel is pressurized as it flows from the upstream side to the downstream side of the pump flow paths 244, 246. While the impeller 236 is rotating, the pressure of the fuel in the pump flow path 244 becomes higher than the pressure of the fuel in the pump flow path 246. The pump flow paths 244, 246 are formed in the top and bottom surfaces of the impeller 236, so the impeller 236 is subject to a force as a result of the difference in pressure of the fuel flowing in the first pump flow path 244 and the second pump flow path 246. In other words, as a result of the difference in pressure of the fuel flowing in the pump flow paths 244, 246, the impeller 236 is subject to a force that presses the impeller 236 towards the casing surface 240 b.

Also, a minute amount of the fuel expelled from the pump unit 214 into the motor unit 212 flows into the clearance between the top surface of the impeller 236 and the casing surface 238 b through the gap between the shaft 220 and a bearing 228. The pressure of the minute amount of fuel that has flowed into this clearance is high, so a force is applied to the impeller 236 in the direction of the casing surface 240 b as a result of the pressure of this fuel.

Also, a minute amount of fuel flows into the clearance between the bottom surface of the impeller 236 and the casing surface 240 b. Fuel that has flown into the clearance is drawn into the group of depression-shaped grooves 236 c, 236 c, . . . The fuel drawn into the depression-shaped grooves 236 c, 236 c, . . . is guided by one wall 237 b of the depression-shaped grooves 236 c, 236 c, . . . and flows towards the end 237 a of the depression-shaped grooves 236 c, 236 c, . . . near the outer periphery (refer to FIG. 16). The fuel within the depression-shaped grooves 236 c, 236 c, . . . that is propelled from near the center towards the outer periphery presses against the casing surface 240 b, generating a lift force on the impeller 236 (i.e., a force acting in the direction to increase the clearance between the impeller 236 and the casing surface 240 b). On the other hand, depression-shaped grooves are not formed on the top surface of the impeller 236, so no lift force is generated between the top surface of the impeller 236 and the casing surface 238 b.

In this way, a force as a result of the pressure difference of the fuel in pump flow paths 244, 246, a force as a result of the pressure of fuel that has flowed upstream from the motor unit 212 to the pump unit 214 through the gap between the shaft 220 and the bearing 228, and a force due to the group of depression-shaped grooves 236 c, 236 c, . . . act on the impeller 236. The force due to the pressure difference of the fuel and the force due to the pressure of the fuel that has flowed upstream act in a direction that presses the impeller 236 towards the casing surface 240 b. The lift force due to the group of depression-shaped grooves 236 c, 236 c, . . . acts in a direction to cancel out the forces pressing the impeller 236 towards the casing surface 240 b. Therefore, the impeller 236 can rotate without being pressed towards the casing surface 240 b. In this way, contact of the impeller 236 with the casing surface 240 b is suppressed, and friction losses and wear can be reduced.

As explained above, in the Wesco pump 210, depression-shaped grooves 236 c, 236 c, . . . are formed in the bottom surface of the impeller 236, and depression-shaped grooves are not formed in the top surface of the impeller 236 and the casing surface 238 b. Therefore, it is possible to cancel out the forces acting to press the impeller 236 towards the casing surface 240 b by the lift forces generated by the depression-shaped grooves 236 c, 236 c, . . . In this way, pressing of the impeller 236 towards the casing surface 240 b and contact with the casing surface 240 b can be suppressed.

Also, in the Wesco pump 210, a projecting portion 238 c is formed in the casing surface 238 b to the inside of the group of concavities 236 b, 236 b, . . . as a continuous loop in the circumferential direction of the impeller 236. At the projecting portion 238 c, the clearance with the impeller 236 is smaller than in other parts, so the flow of fuel leaking from the pump flow path past the projecting portion 238 c into the clearance on the discharge hole side is suppressed. Therefore, the quantity of fuel leaking from the pump fuel path 244 can be reduced. In this way, the fuel within the casing can be efficiently pressurized, and high pump performance can be achieved.

Also, even if the force acting on the impeller 236 toward the casing surface 238 b increases due to fluctuations of the fuel pressure within the pump flow paths 244, 246, contact of the impeller 236 with the casing surface 240 b is suppressed by the pressure of the fuel that has flowed from the motor unit 212 to the pump unit 214 through the gap between the shaft 220 and the bearing 228. Also, even assuming the impeller 236 and the casing surface 238 b contacted, the impeller 236 will just contact the projecting portion 238 c, so it is possible to minimize and suppress the friction losses when the impeller and the casing contact.

Fifth Representative Embodiment

In the Wesco pump 210 according to the fourth representative embodiment as described above, depression-shaped grooves are only formed on the bottom surface of the impeller 236, but depression-shaped grooves may also be formed in the top surface of the impeller. The following is a description of a Wesco pump 310 according to a fifth representative embodiment, in which depression-shaped grooves are formed in the top surface of the impeller. The explanation is either omitted or simplified for parts that overlap with the fourth representative embodiment.

The Wesco pump 310 according to the fifth representative embodiment also includes a motor unit and a pump unit 314. The motor unit has the same configuration as the Wesco pump 10 according to the first representative embodiment. The pump unit 314 includes a substantially disk-shaped impeller 336 and a pump casing 339 that houses the impeller 336.

The configuration of the impeller 336 is substantially similar to the impeller 236 according to the fourth representative embodiment. That is, a group of concavities 336 b, 336 b, . . . is formed in the top surface of the impeller 336. In the bottom surface of the impeller 336, a group of concavities 336 a, 336 a, . . . and a group of depression-shaped grooves 336 c, 336 c, . . . are formed.

Also, a group of depression-shaped grooves 336 d, 336 d, . . . is formed in the top surface of the impeller 336. As shown in FIG. 19, the depression-shaped grooves 336 d are formed in the same shape as the depression-shaped grooves 336 c formed in the bottom surface of the impeller 336. That is, the depression-shaped grooves 336 d extend from an end near the center to an end towards the periphery in a curved shape (spiral shape) However, the number of depression-shaped grooves 336 d is fewer than the number of depression-shaped grooves 336 c (refer to FIGS. 15 and 19).

The pump casing 339 includes a pump cover 338 and a pump body 340. A casing surface 340 b, groove 340 a, and intake hole 342 of the pump body 340 are formed in the same way as those of the pump body 240 according to the fourth representative embodiment. The casing surface 338 b of the pump cover 338 is formed in a plane shape parallel to the top surface of the impeller 336, as shown in FIG. 18. Also, the groove 338 a and the discharge hole 350 of the pump cover 338 are formed in the same way as the pump cover 238 according to the fourth representative embodiment. A first pump flow path 344 is formed by the group of concavities 336 b formed in the top surface of the impeller 336 and the groove 338 a formed in the pump cover 338. A second pump flow path 346 is formed by the group of concavities 338 a formed in the bottom surface of the impeller 336 and the groove 340 a formed in the pump body 340.

Here the forces acting on the impeller 336 when the impeller 336 rotates are explained. A force due to the pressure difference of the fuel flowing in the first pump flow path 344 and the second pump flow path 346 acts on the impeller 336, as for the fourth representative embodiment. Also, a force acts as a result of fuel that flows from the motor unit into the clearance between the top surface of the impeller 336 and the casing surface 338 b through the gap between the shaft and the bearing. These forces act in a direction that presses the impeller 336 towards the casing surface 340 b.

Also, the group of depression-shaped grooves 336 c, 338 c, . . . formed in the bottom surface of the impeller 336 generates a lift force B. The lift force B acts in a direction to increase the clearance between the bottom surface of the impeller 336 and the casing surface 340 b.

Furthermore, the group of depression-shaped grooves 336 d, 336 d, . . . formed in the top surface of the impeller 336 generate a lift force C acting in a direction to increase the clearance between the top surface of the impeller 336 and the casing surface 338 b. As stated above, the number of grooves in the group of depression-shaped grooves 336 d, 336 d, . . . is fewer than the number of grooves in the group of depression-shaped grooves 336 c, 336 c, . . . Therefore, the lift force C is smaller than the lift force B.

In this way, when the impeller 336 rotates, a force due to the pressure difference of the fuel flowing in the pump flow paths 344, 346, a force due to the pressure of the fuel that has flowed from the motor unit into the pump casing 339, the lift force B, and the lift force C act on the impeller 336. The force due to the pressure difference of the fuel, the pressure of the fuel that has flowed upstream, and the lift force C act in a direction to press the impeller 336 towards the casing surface 340 b. The lift force B acts in a direction to cancel out these forces. The lift force B is larger than the lift force C, so the force obtained by subtracting the force C from the force B can act to cancel the force due to the pressure difference of the fuel and force due to the pressure of the fuel that has flowed upstream. Therefore, contact of the impeller 336 with the casing surface 340 b can be suppressed, and the impeller 336 can rotate smoothly. In this way, it is possible to improve the efficiency of the pump.

Also, if the impeller 336 is pressed against the casing surface 338 b as a result of fluctuations in fuel pressure, the clearance between the top surface of the impeller 336 and the casing surface 338 b is reduced. Then the fuel in this clearance is compressed, and the lift force C increases. The impeller 336 is pressed by the increased lift force C to return to the original position. Therefore, contact between the impeller 336 and the casing surface 338 b is suppressed.

In the fifth representative embodiment as described above, by making the number of grooves in the group of depression-shaped grooves 336 d, 336 d, . . . fewer than the number of grooves in the group of depression-shaped grooves 336 c, 336 c, . . . the magnitude of the lift force C (i.e., the force pressing the impeller downwards) was made smaller than the lift force B (i.e., the force pressing the impeller upwards). However, the present teachings are not limited to this form. For example, as shown in FIG. 20, the length of the depression-shaped grooves 436 d in the top surface of the impeller may be made shorter than the length of the depression-shaped grooves in the bottom surface of the impeller. Also, as shown in FIG. 21, the width of the depression-shaped grooves 536 d in the top surface of the impeller may be made smaller than the width of the depression-shaped grooves in the bottom surface of the impeller. Or, as shown in FIG. 22, the inflow angle (in other words, the angle θ formed between the depression-shaped grooves and the direction of flow of fuel within the clearance (refer to FIG. 23)) of the depression-shaped groove 636 d in the top surface of the impeller may be made larger than the inflow angle of the depression-shaped grooves in the bottom surface of the impeller. Also, the depth of the depression-shaped grooves in the top surface of the impeller may be made shallower than the depth of the depression-shaped grooves in the bottom surface of the impeller. In this way, by determining the shape of the depression-shaped grooves on the top surface of the impeller in accordance with the shape of the depression-shaped grooves on the bottom surface of the impeller, it is possible to make the lift force C smaller than the lift force B.

Also, in each of the representative embodiments described above, the depression-shaped grooves formed in either the impeller or in the pump casing extend from near the center of the impeller towards the outer periphery in a curved shape (spiral shape). However, the present teachings are not limited to this form. The number, length, cross-sectional shape of the depression-shaped grooves formed in the impeller or in the pump casing may be appropriately designed.

Finally, although the preferred embodiments have been described in detail, the present embodiments arc for illustrative purpose only and not restrictive. It is to be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims. In addition, the additional features and aspects disclosed herein also may be utilized singularly or in combination with the above aspects and features. 

1. A pump comprising a casing and a substantially disk-shaped impeller rotating within the casing, wherein a group of concavities is formed on both front and reverse surfaces of the impeller, concavities forming each group are repeated in a circumferential direction of the impeller, a first groove is formed on a first casing internal surface in opposition to the front surface of the impeller, the first groove extending from an upstream end to a downstream end in an area facing one of the groups of concavities of the impeller, a second groove is formed on a second casing internal surface in opposition to the reverse surface of the impeller, the second groove extending from an upstream end to a downstream end in an area facing the other of the groups of concavities of the impeller, an intake hole and a discharge hole are formed in the casing, the intake hole linking the upstream end of one of the first groove and the second groove with the outside of the casing, the discharge hole linking the downstream end of the other of the first groove and the second groove with the outside of the casing, and a group of depression-shaped grooves is formed in at least the first and second casing internal surfaces, each depression-shaped grooves extends from the center towards the outer periphery while shifting in the direction of rotation of the impeller, and the group of depression-shaped grooves is asymmetrically formed with respect to the axis of rotation of the impeller in accordance with the position of the first and second grooves.
 2. A pump according to claim 1, wherein in the area near the discharge hole in the casing internal surface and/or in the area near the intake hole in the casing internal surface, the lift forces generated on the impeller by the group of depression-shaped grooves are greater than in other areas.
 3. A pump according to claim 1, wherein the group of depression-shaped grooves is formed only in the area near the discharge hole and/or in the area near the intake hole.
 4. A pump according to claim 3, wherein each depression-shaped groove forming the group of depression-shaped grooves extends from the center of the impeller towards the outer periphery of the impeller in a spiral shape.
 5. A pump comprising a casing and a substantially disk-shaped impeller rotating within the casing, wherein a group of concavities is formed on both front and reverse surfaces of the impeller, concavities forming each group are repeated in a circumferential direction of the impeller, a first groove is formed on a first casing internal surface in opposition to the front surface of the impeller, the first groove extending from an upstream end to a downstream end in an area facing one of the groups of concavities of the impeller, a second groove is formed on a second casing internal surface in opposition to the reverse surface of the impeller, the second groove extending from an upstream end to a downstream end in an area facing the other of the groups of concavities of the impeller, an intake hole and a discharge hole are formed in the casing, the intake hole linking the upstream end of one of the first groove and the second groove with the outside of the casing, the discharge hole linking the downstream end of the other of the first groove and the second groove with the outside of the casing, in at least one surface from among the front and reverse surfaces of the impeller and the first and second casing internal surfaces, depression-shaped grooves are formed so that fluid in the clearance between the impeller and the casing is pressurized and a force is generated in the direction that increases the clearance between the impeller and the casing when the impeller rotates, and the clearance between the surface on which the depression-shaped grooves are formed and the surface in opposition thereto when the impeller is not inclined with respect to the casing increases from the center of the impeller towards the outer periphery of the impeller.
 6. A pump according to claim 5, wherein one surface from among the surface in which the depression-shaped grooves is formed and the surface in opposition thereto is formed as a flat plane, and the other surface is formed in a tapered shape so that the clearance with the impeller increases from the center of the impeller towards the outer periphery of the impeller.
 7. A pump according to claim 6, wherein the depression-shaped grooves extend from the center of the impeller towards the outer periphery of the impeller in a spiral shape.
 8. A pump comprising a casing and a substantially disk-shaped impeller rotating within the casing, wherein a group of concavities is formed on both front and reverse surfaces of the impeller, concavities forming each group are repeated in a circumferential direction of the impeller, a first groove is formed on a first casing internal surface in opposition to the front surface of the impeller, the first groove extending from an upstream end to a downstream end in an area facing one of the groups of concavities of the impeller, a second groove is formed on a second casing internal surface in opposition to the reverse surface of the impeller, the second groove extending from an upstream end to a downstream end in an area facing the other of the groups of concavities of the impeller, an intake hole and a discharge hole are formed in the casing, the intake hole linking the upstream end of a pump flow path formed by the groups of concavities, the first groove, and the second groove with the outside of the casing, the discharge hole linking the downstream end of the pump flow path with the outside of the casing, depression-shaped grooves sealed from the pump flow path are formed on at least one surface from among the intake hole side impeller surface and the intake hole side casing internal surface, and depression-shaped grooves sealed from the pump flow path are formed in neither the discharge hole side impeller surface nor the discharge hole side casing internal surface.
 9. A pump according to claim 8, wherein a projecting portion is formed in the discharge hole side casing internal surface as a loop in the circumferential direction of the impeller.
 10. A pump according to claim 9, wherein the depression-shaped grooves extend from the center of the impeller towards the outer periphery of the impeller in a spiral shape.
 11. A pump according to claim 8, further comprising a motor chamber provided on the outside of the casing, and a motor housed within the motor chamber, wherein the motor includes a shaft that rotates, the discharge hole links the pump flow path and the motor chamber, a through hole that is penetrated by the motor shaft are formed in the casing, and one end of the motor shaft is fitted to the impeller.
 12. A pump comprising a casing and a substantially disk-shaped impeller rotating within the casing, wherein a group of concavities is formed on both front and reverse surfaces of the impeller, concavities forming each group are repeated in a circumferential direction of the impeller, a first groove is formed on a first casing internal surface in opposition to the front surface of the impeller, the first groove extending from an upstream end to a downstream end in an area facing one of the groups of concavities of the impeller, a second groove is formed on a second casing internal surface in opposition to the reverse surface of the impeller, the second groove extending from an upstream end to a downstream end in an area facing the other of the groups of concavities of the impeller, an intake hole and a discharge hole are formed in the casing, the intake hole linking the upstream end of a pump flow path formed by the groups of concavities, the first groove, and the second groove with the outside of the casing, the discharge hole linking the downstream end of the pump flow path with the outside of the casing, intake hole side depression-shaped grooves are formed on at least one surface from among the intake hole side impeller surface and the intake hole side casing internal surface so that when the impeller rotates fluid is pressurized and a lift force is generated that acts in the direction to increase the clearance between the intake hole side impeller surface and the intake hole side casing internal surface, discharge hole side depression-shaped grooves are formed on at least one surface from among the discharge hole side impeller surface and the discharge hole side casing internal surface so that when the impeller rotates fluid is pressurized and a lift force is generated that acts in the direction to increase the clearance between the discharge hole side impeller surface and the discharge hole side casing internal surface, and the number and/or shape of the discharge hole side depression-shaped grooves are determined so that the lift force generated is smaller than the lift force generated by the intake hole side depression-shaped grooves, in accordance with the number and/or shape of the intake hole side depression-shaped grooves. 